[parisc-linux] MAX_ADDRESS.

[parisc-linux] MAX_ADDRESS.

[Naresh]

Hi,
This question is relevant to the 2.4 kernel. Is MAX_ADDRESS really the
highest virtual address mapped by the kernel? I can see this comment in
'paging_init()' in the section for DISCONTIGMEM. However,
pagetable_init() doesnt make a check before it calls 'map_pages( )' for
all the ranges of memory. So we may DISCONTIGMEM turned off but  it may
so happen that we have a 'pmem_ranges[]' entry that is greater than
MAX_ADDRESS which may find its way into the kernel page tables.
Regards,
Naresh.

Re: [parisc-linux] MAX_ADDRESS.

[Matthew Wilcox]

On Tue, Sep 30, 2003 at 11:03:28AM +0530, Naresh wrote:
> This question is relevant to the 2.4 kernel. Is MAX_ADDRESS really the
> highest virtual address mapped by the kernel? I can see this comment in
> 'paging_init()' in the section for DISCONTIGMEM. However,
> pagetable_init() doesnt make a check before it calls 'map_pages( )' for
> all the ranges of memory. So we may DISCONTIGMEM turned off but  it may
> so happen that we have a 'pmem_ranges[]' entry that is greater than
> MAX_ADDRESS which may find its way into the kernel page tables.

Ignore the DISCONTIGMEM code.  It's completely broken (and we offer no
way to turn CONFIG_DISCONTIGMEM on).

I'm not sure what half of this code is for; you'd need to ask John Marvin
who wrote it.

-- 
"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk

Re: [parisc-linux] MAX_ADDRESS.

[Naresh]

MAX_ADDRESS has nothing to do with DISCONTIGMEM. Its definition is generic(
pgtable.h), although it is not used anywhere. I just happened to see the comment in
the DISCONTIGMEM code. Even if DISCONTIGMEM is turned off, there is no check for
MAX_ADDRESS before the call to 'map_pages()' in 'pagetable_init( )', which is why I
would like to know if MAX_ADDRESS can be ignored.

Regards,
Naresh.

Matthew Wilcox wrote:

> On Tue, Sep 30, 2003 at 11:03:28AM +0530, Naresh wrote:
> > This question is relevant to the 2.4 kernel. Is MAX_ADDRESS really the
> > highest virtual address mapped by the kernel? I can see this comment in
> > 'paging_init()' in the section for DISCONTIGMEM. However,
> > pagetable_init() doesnt make a check before it calls 'map_pages( )' for
> > all the ranges of memory. So we may DISCONTIGMEM turned off but  it may
> > so happen that we have a 'pmem_ranges[]' entry that is greater than
> > MAX_ADDRESS which may find its way into the kernel page tables.
>
> Ignore the DISCONTIGMEM code.  It's completely broken (and we offer no
> way to turn CONFIG_DISCONTIGMEM on).
>
> I'm not sure what half of this code is for; you'd need to ask John Marvin
> who wrote it.
>
> --
> "It's not Hollywood.  War is real, war is primarily not about defeat or
> victory, it is about death.  I've seen thousands and thousands of dead bodies.
> Do you think I want to have an academic debate on this subject?" -- Robert Fisk
> _______________________________________________
> parisc-linux mailing list
> parisc-linux@lists.parisc-linux.org
> http://lists.parisc-linux.org/mailman/listinfo/parisc-linux

Re: [parisc-linux] MAX_ADDRESS.

[James Bottomley]

On Tue, 2003-09-30 at 07:24, Naresh wrote:
> MAX_ADDRESS has nothing to do with DISCONTIGMEM. Its definition is generic(
> pgtable.h), although it is not used anywhere. I just happened to see the comment in
> the DISCONTIGMEM code. Even if DISCONTIGMEM is turned off, there is no check for
> MAX_ADDRESS before the call to 'map_pages()' in 'pagetable_init( )', which is why I
> would like to know if MAX_ADDRESS can be ignored.

No.  It does represent the highest virtual address possible.

Linux has 3 levels of page tables, so on a 64 bit kernel (8 bytes per
pte and 8 bytes per pte page pointer etc), we can address a maximum of
512GB with 4k pages.

James